Firstly, ensure the seats are from the correct age car - 3 different eras of seat were fitted to Omegas, and they are not cross compatible:

Prefacelift (94-97). Mechanical pretensioners, simple heating, no active restraints, no side airbags
Minifacelift (98-99). Pyrotechnic pretensioners, simple heating, no active restraints, side airbags
Facelift (00-03). Pyrotechnic pretensioners, advanced heating, active head restraints, side airbags

Feature	PFL	MFL	FL
Belt Pretensioners	Mechnical	Pyrotechnic	Pyrotechnic
Side airbag	No	Yes	Yes
Active Head Restraint	No	No	Yes
Seat Heating	Simple	Simple	Advanced

So, assuming you are not retarded enough to want to disable safety systems (which would affect NCAP ratings, and insurance premiums), the only ones you can swap are ones from the same era.

The only exception is fitting FL into MFL if you dont mind the heaters not working (but NOT the other way around)



The passenger seat will just just plug in.  The Drivers seat needs a minor modification underneath, see image below:



Find the connector pictured. The large Red, smaller Red and the small Black all need to be soldered together, and the Large Brown and the small Brown need to be soldered together.  Note, the brown with a white trace should not be modified!  Blacks going to other connectors shouldn't be modified either - all modifications are done on this 1 single connector (X46 on wiring diagrams).

Thats it! No modifications at the sill wiring, and car loom all stays in tact